In the prior art system which preceded the development of the present invention, a pressure lock was positioned below the cooker auger and received cooked cereal dough from a continuous cooker. The pressure lock maintained the elevated pressure on the dough in the cooker. The dough was discharged from the cooker through the pressure lock to size-reducing equipment operated at ambient pressure. The lock comprised a lock auger, a large cylindrical metal rotor, and a fixed housing which held the rotor. The rotor was a heavy metal cylinder having a plurality of spaced holes bored through the rotor, having central axes equidistantly spaced from the center of rotation of the rotor. The holes were separated by the solid mass of the rotor. Each of the holes was of about the same diameter as a passage from the lock auger to the size-reducing equipment. The distances between the holes were at least sufficient to block off the noted passage.
The rotor was turned continuously within the fixed housing, with the rate of rotation adjusted to best approximate the actual need for opening and closing. In the open position, the rotor was turned about its center of rotation sufficiently to permit one hole in the rotor to align with the passage from the lock auger. In the closed position, the rotor was oriented so that the solid rotor surface between the holes, blocked the passage. Between these two positions, the lock was neither fully open nor fully closed.
While the above device has operated successfully for many years, it has been observed that great quantities of steam are lost due to the manner of opening and closing the pressurized passage. Indeed, because the locks opened on a timed cycle, they opened whether or not food was present. Moreover, frictional forces caused excessive wear of the parts and, if cleaning was not rigorous, cereal dough could become caked on the equipment where it burned and flaked off into the cereal as unsightly dark spots. Investigations of various equipment makers to find a suitable replacement were not successful.
Accordingly, there is a present need for an improved pressure lock to permit discharge of cereal doughs from continuous cookers without the problems of the prior art.